Add Git commit ID tracking to health endpoint

Features:
- Health endpoint now returns git_commit SHA and version
- Auto-detects git commit during Docker build
- Falls back to 'unknown' if git info unavailable
- Allows AI agents to verify deployed version

Changes:
1. server.js: Add git_commit and version to /health response
2. Dockerfile: Add git installation and commit detection
3. Dockerfile: Accept GIT_COMMIT and APP_VERSION build args
4. docker-compose.yml: Pass build args and env vars for versioning
5. README.md: Document version tracking in health endpoint

Example response:
{
  "status": "healthy",
  "postgres": "connected",
  "redis": "connected",
  "timestamp": "2026-02-14T10:30:00.000Z",
  "git_commit": "eb6b6e0a1b2c3d4e5f6g7h8i9j0k1l2m3n4o5p6q",
  "version": "1.0.0"
}

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

README.md

@@ -275,13 +275,25 @@ saac deployments
 ### Step 7: Verify Deployment
 
 ```bash
-# Check health endpoint
+# Check health endpoint (includes git commit ID)
 curl https://template-001.startanaicompany.com/health
 
+# You should see a response like:
+# {
+#   "status": "healthy",
+#   "postgres": "connected",
+#   "redis": "connected",
+#   "timestamp": "2026-02-14T10:30:00.000Z",
+#   "git_commit": "eb6b6e0...",
+#   "version": "1.0.0"
+# }
+
 # View the website
 curl https://template-001.startanaicompany.com
 ```
 
+**Note:** The `git_commit` field in the health endpoint shows which version is deployed, making it easy for AI agents to track deployments.
+
 ---
 
 ## Architecture
@@ -395,7 +407,7 @@ Returns the main template website with information about the deployment.
 
 ### GET /health
 
-Health check endpoint that verifies connections to PostgreSQL and Redis.
+Health check endpoint that verifies connections to PostgreSQL and Redis, and returns deployment version information.
 
 **Response:**
 ```json
@@ -403,7 +415,9 @@ Health check endpoint that verifies connections to PostgreSQL and Redis.
   "status": "healthy",
   "postgres": "connected",
   "redis": "connected",
-  "timestamp": "2026-02-14T10:30:00.000Z"
+  "timestamp": "2026-02-14T10:30:00.000Z",
+  "git_commit": "eb6b6e0a1b2c3d4e5f6g7h8i9j0k1l2m3n4o5p6q",
+  "version": "1.0.0"
 }
 ```
 
@@ -411,10 +425,18 @@ Health check endpoint that verifies connections to PostgreSQL and Redis.
 ```json
 {
   "status": "unhealthy",
-  "error": "Connection error message"
+  "error": "Connection error message",
+  "git_commit": "eb6b6e0a1b2c3d4e5f6g7h8i9j0k1l2m3n4o5p6q",
+  "version": "1.0.0"
 }
 ```
 
+**Version Tracking:**
+- `git_commit`: The Git commit SHA of the deployed code (auto-detected during build)
+- `version`: Application version (defaults to 1.0.0, can be set via APP_VERSION env var)
+
+This allows AI agents and monitoring tools to verify which version is currently running.
+
 ---
 
 ## Troubleshooting